Xamarin project not running, netstandard2.0 error

Im learning Xamarin, when I try to create a project and build it, it gives me this error:

The "Xamarin.Forms.Build.Tasks.GetTasksAbi" task could not be loaded from the assembly , C:\Users\XXXX.nuget\packages\xamarin.forms\3.0.0.482510\build\netstandard2.0\Xamarin.Forms.Build.Tasks.dll. Could not load file or assembly 'netstandard, Version=2.0.0.0, Culture=neutral

I really dont know how to solve it. I also tried: docs.microsoft.com/en-us/xamarin/xamarin-forms/internals/net-standard